1. Field of the Invention
The present invention relates to a physical quantity estimation device for estimating a physical quantity relating to the ease of slippage between a wheel and the surface of a road, and particularly to a physical quantity estimation device capable of accurately estimating a physical quantity relating to the ease of slippage between a road surface and a wheel even when an unsprung resonance phenomenon is generated, and to an ABS control device for controlling braking pressure using this physical quantity estimation device.
2. Description of the Related Art
Japanese Patent Application Laid-Open (JP-A) No. 10-114263 (corresponding to U.S. Pat. No. 6,122,585) discloses an anti-lock braking system (ABS) control device for performing, on the basis of a wheel deceleration dynamic model, a calculation to estimate the torque gradient, i.e. the road surface xcexc gradient (the change of the road surface xcexc to the change of the slip) from the time series data of a wheel velocity signal, and for then controlling the manipulation variable of the braking force so that the road surface xcexc gradient is 0.
When a vehicle travels from an icy road surface onto a dry road surface while the braking force is being controlled so as to be at the maximum amount by the above described ABS control device, then, as is shown in FIG. 1A, an oscillation phenomenon is generated in the wheel velocity. This wheel velocity oscillation phenomenon causes the accuracy of the xcexc gradient estimation to be reduced. As is shown in FIG. 1B, in some cases, a delay in the adaptation of the ABS control is also generated.
The present inventors discovered that this phenomenon of oscillation in the wheel velocity is due to resonance movement between the tires and the suspension in the longitudinal direction of the vehicle.
The present invention is based on the above discovery and aims to provide a physical quantity estimating device capable of accurately estimating a physical quantity relating to the ease of slippage between a wheel and the surface of a road even when longitudinal resonance movement is generated between the tires and the suspension.
In order to achieve the above aim, the present invention comprises: wheel velocity detection means for detecting a wheel velocity and outputting a wheel velocity signal; and physical quantity estimation means for identifying a parameter of a physical model representing unsprung resonance characteristics from the wheel velocity signal, and estimating a physical quantity relating to ease of slippage between a road surface and a wheel from the identified parameter.
According to the present invention, the wheel velocity is detected by the wheel velocity detection means and a wheel velocity signal is output. The physical quantity estimation means identifies the parameter of a physical model representing the unsprung resonance from the wheel velocity signal and estimates a physical quantity relating to the ease of slippage between the road surface and the wheel from the identified parameter.
The physical model of the present invention can be a resonance model which has the unsprung resonance frequency as the undamped natural frequency. In this case, the physical quantity estimation means estimates a physical quantity relating to the ease of slippage between the road surface and the wheel on the basis of the damping ratio of the resonance model.
In the present invention, because a parameter of a physical model representing unsprung resonance characteristics is identified and a physical quantity relating to the ease of slippage between the road surface and a wheel is estimated from the identified parameter, the physical quantity can be accurately estimated even when an unsprung resonance phenomenon is generated.
The present invention is capable of being used in an ABS control device for controlling braking pressure on the basis of the estimated physical quantity.